Dilation system

ABSTRACT

A dilation system for accessing a surgical target site to perform surgical procedures. In one version, the dilation system includes a dilation assembly and an actuating mechanism. The dilation assembly comprises plurality of dilator segments. The actuating mechanism is operably associated with the dilator segments so as to cause the dilator segments to move from a collapsed state to an expanded state.

BACKGROUND

Dilators are known devices for creating surgical access sites. Once anoperative level is identified and an incision is created, dilators areused to create a surgical access site which is often followed by the useof a retractor or other specialized tools to create a surgical accesscorridor.

When accessing certain areas of a patient, it is desirable to avoidneural elements or nerves. For example, during a lateral approach to apatient's spine, a psoas muscle, which is located on either side of thespine, is separated in order to access the spine and, in particular, anintervertebral disc space or one or more vertebral bodies within apatient's spinal column. It is desirable to avoid neural elements ornerves of the lumbar plexus that lie within the psoas muscle during suchprocedures. The anterior third of the psoas muscle is typicallyconsidered a safe zone for muscle separation.

The neural elements or nerves of the psoas muscle may be mapped using aprobe. In this manner, the most posterior neural or nerve free area ofthe psoas muscle may be located and identified. The probe may then beinserted through the psoas muscle via the most posterior neural or nervefree tissue area or through nearly any other region that is free ofneural elements or nerves and toward the spine or into theintervertebral disc space in order to initiate safe tissue separation ofthe psoas muscle. Dilators are next placed over the probe to create andenlarge a surgical access site. Following the use of dilators, aretractor or other specialized tools are used to further enlarge thesurgical access corridor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a dilation system constructed inaccordance with the inventive concepts disclosed herein.

FIG. 2A is a partial cross sectional, side elevational view of thedilation system of FIG. 1 shown in a collapsed state.

FIG. 2B is a partial cross sectional, side elevational view of thedilation system of FIG. 1 shown in an expanded state.

FIG. 3A is a cross sectional view taken along line 3A-3A of FIG. 2A.

FIG. 3B is a cross sectional view taken along line 3B-3B of FIG. 2B.

FIG. 4 is an exploded, perspective view of a dilator assembly.

FIG. 5 is a perspective view of one version of a dilator segment.

FIG. 6 is a perspective view of another version of a dilator segment.

FIG. 7 a side elevational view of another embodiment of an actuatinghandle for use in the dilation system of FIG. 1.

FIG. 8 is a flow chart of an exemplary method for forming an accessopening through a muscle in a patient's spine.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Before explaining at least one embodiment of the presently disclosed andclaimed inventive concepts in detail, it is to be understood that thepresently disclosed and claimed inventive concepts are not limited intheir application to the details of construction, experiments, exemplarydata, and/or the arrangement of the components set forth in thefollowing description or illustrated in the drawings. The presentlydisclosed and claimed inventive concepts are capable of otherembodiments or of being practiced or carried out in various ways. Also,it is to be understood that the phraseology and terminology employedherein is for purpose of description and should not be regarded aslimiting.

In the following detailed description of embodiments of the inventiveconcepts, numerous specific details are set forth in order to provide amore thorough understanding of the inventive concepts. However, it willbe apparent to one of ordinary skill in the art that the inventiveconcepts within the disclosure may be practiced without these specificdetails. In other instances, certain well-known features may not bedescribed in detail to avoid unnecessarily complicating the instantdisclosure.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having,” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but may include otherelements not expressly listed or inherently present therein.

Unless expressly stated to the contrary, “or” refers to an inclusive orand not to an exclusive or. For example, a condition A or B is satisfiedby anyone of the following: A is true (or present) and B is false (ornot present), A is false (or not present) and B is true (or present),and both A and B are true (or present).

The term “and combinations thereof” as used herein refers to allpermutations or combinations of the listed items preceding the term. Forexample, “A, B, C, and combinations thereof” is intended to include atleast one of: A, B, C, AB, AC, BC, or ABC, and if order is important ina particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB.Continuing with this example, expressly included are combinations thatcontain repeats of one or more item or term, such as BB, AAA, AAB, BBC,AAABCCCC, CBBAAA, CABABB, and so forth. A person of ordinary skill inthe art will understand that typically there is no limit on the numberof items or terms in any combination, unless otherwise apparent from thecontext.

In addition, use of the “a” or “an” are employed to describe elementsand components of the embodiments herein. This is done merely forconvenience and to give a general sense of the inventive concepts. Thisdescription should be read to include one or at least one and thesingular also includes the plural unless it is obvious that it is meantotherwise.

The use of the terms “at least one” and “one or more” will be understoodto include one as well as any quantity more than one, including but notlimited to each of, 2, 3, 4, 5, 10, 15, 20, 30, 40, 50, 100, and allintegers and fractions, if applicable, therebetween. The terms “at leastone” and “one or more” may extend up to 100 or 1000 or more, dependingon the term to which it is attached; in addition, the quantities of100/1000 are not to be considered limiting, as higher limits may alsoproduce satisfactory results.

Further, as used herein any reference to “one embodiment” or “anembodiment” means that a particular element, feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. The appearances of the phrase “in oneembodiment” in various places in the specification are not necessarilyall referring to the same embodiment.

As used herein qualifiers such as “about,” “approximately,” and“substantially” are intended to signify that the item being qualified isnot limited to the exact value specified, but includes some slightvariations or deviations therefrom, caused by measuring error,manufacturing tolerances, stress exerted on various parts, wear andtear, and combinations thereof, for example.

As used herein, the term “patient” is meant to include all organisms,whether alive or dead, including any species having soft tissues andbones. For example, a method according to the inventive conceptsdisclosed herein may be used to repair a spinal injury in a livinghuman, horse, cow, sheep, cat, dog, and the like. In another example, amethod according to the inventive concepts disclosed herein may be usedin a non-living organism to train medical personnel in surgicaltechniques.

Certain exemplary embodiments of the invention will now be describedwith reference to the drawings. In general, such embodiments relate todilation systems, and more particularly, to dilation systems foraccessing a patient's spinal column. As generally understood by one ofordinary skill in the art, the dilation systems will be described inconnection with accessing the spine to perform a surgical procedure, butthe dilation systems will find use not only in orthopedic surgery, butin other surgical procedures in which a surgeon wishes to gain access toan internal cavity by cutting the skin and going through the body wallin order to keep the incision spread apart so that surgical instrumentscan be inserted. For example, the dilation systems may be used foranteriorly or posteriorly accessing the spine, for accessing the lumbar,thoracic, or cervical region of the spine, or for accessing nearly anyother part of the body.

Referring to FIGS. 1, 2A, 2B, 3A, and 3B, a dilation system 10 isillustrated. The dilation system 10 may aid in performing surgicalprocedures and, more particularly, but not by way of limitation, may aidin accessing a surgical target site to perform surgical procedures. Insome embodiments, the dilation system 10 may be used to create aninitial corridor within a patient (e.g., 4-10 mm) which may be expandedto a desired diameter (e.g., 16-22 mm) without inserting any additionalinstruments. In some embodiments, the dilation system 10 may be used incombination with a guide, such as a K-wire or a monitoring probe, asfurther described herein.

The dilation system 10 includes a dilator assembly 12 and an actuatingmechanism 14. The dilator assembly 12 may include a plurality of dilatorsegments 16. The actuating mechanism 14 is capable of moving the dilatorsegments 16 radially outwardly in a way to cause the dilator segments 16to move between a collapsed state (FIGS. 1, 2A, and 3A) and an expandedstate (FIGS. 2B and 3B) such that, in use, an initial corridor within apatient may be expanded to a desired diameter.

The dilator assembly 12 may include two or more dilator segments 16. Forexample, the dilator assembly 12 may include any number of dilatorsegments 16, such as, for example, two, three, four, and the like. Thedilator assembly 12 is illustrated herein as having four dilatorsegments 16. The contour of the dilator segments 16, when assembled, mayform a generally circular cylinder having a bore 20 extending the lengthof the dilator segments 16 from a proximal end 22 to a distal end 24 ofthe dilator assembly 12. It will be appreciated, however, that thedilator segments 16 may be configured to form other shapes, such as anoval shaped cylinder.

Referring to FIG. 4, each dilator segment 16 may be a generallyarc-shaped member having a proximal end 26, a distal end 28, an outerside 30, and an inner side 32. Each dilator segment 16 has a proximaltapered surface 34 extending from the proximal end 22 toward the distalend 24 and a distal tapered surface 36 extending from the distal end 24toward the proximal end 22. The proximal tapered surfaces 34 and thedistal tapered surfaces 36 are generally configured so that componentsof the actuating mechanism 14 may contact and slide along the proximaltapered surfaces 34 and the distal tapered surfaces 36 in a manner to bedescribed below. In one embodiment, the proximal tapered surfaces 34 andthe distal tapered surfaces 36 are generally arc shaped.

The dilator segments 16 may be machined, molded or extruded and machinedfrom materials including, but not limited to, stainless steel, anodizedaluminium, polyether ether ketone (PEEK), carbon fiber composite, and/orany biocompatible material suitable to maintain the shape and functionof the components.

Tension may be applied to the dilator segments 16 by one or moreconstrictors 38 to bias the dilator segments 16 in the collapsed state.Constrictors 38 may be positioned about the dilator segments 16 suchthat, when in the collapsed state, the dilator segments 16 form thecircular cylinder. For example, one or more constrictors 38 in the formof a ring may be positioned about an outer surface 36 of each dilatorsegment 16. In some embodiments, constrictors 38 may be positionedwithin a groove 39 on the outer side 30 of the dilator segments.Constrictors 38 may be positioned between the proximal end 26 and thedistal end 28 of the dilator assembly 12. Exemplary constrictors 38include, but are not limited to, elastic rings, donut springs, expansionsprings, and/or the like.

Referring to FIGS. 3A and 3B, with the dilator assembly 12 in thecollapsed state, the dilator segments 16 may form a circular cylinderhaving the bore 20 extending there through, as illustrated in FIG. 3A.In the collapsed state, the dilator segments 16 may be configured sothat the dilator segments 16 cooperate to form a dilator of a desireddiameter.

FIG. 3B illustrates the dilator assembly 12 in the expanded statewherein the dilator segments 16 are moved radially outward relative tothe collapsed state whereby the outer side 30 of the dilator segments 16cooperate to form a dilator of a desired diameter which is greater thanthe diameter of the dilator in the collapsed state. In some embodiments,the dilator segments 16 move uniformly away from the longitudinal axis.In some embodiments, the dilator segments 16 may be moved from thelongitudinal axis at different distances so that the dilator assembly 12expands a greater amount in a selected direction.

To permit nerve monitoring for the purpose of determining the locationof nerves or neural structures relative to the each of the dilatorsegments 16 as they are advanced over a K-wire (not shown) towards orpositioned at or near the surgical target site and as they are moved tothe expanded state, one or more of the dilator segments 16 may beconfigured to receive a probe (not shown). For example, the dilatorsegments 16 may include a channel 42 (FIG. 5) formed at or near theouter side 30 of the dilator segments 16 and extending the length of thedilator segments 16 for receiving a probe (not shown). Alternatively, asshown in FIG. 6, the one or more of the dilator segments 16 may includean electrode 42 a to enable monitoring of nerves. The dilator segments16 may be equipped with the electrodes 42 a via any number of suitablemethods, including but not limited to providing electrically conductiveelements within the walls of the dilator segments 16 such as bymanufacturing the dilator segments 16 from plastic or similar materialcapable of injection molding or manufacturing the dilators from aluminum(or similar metallic substance) and providing outer insulation layerwith exposed regions (such as by anodizing the exterior of the aluminiumdilator). The dilator segments 16 may include a corresponding connectorpoint for connecting the electrode probe 42 a to neural monitoringequipment. In another version, the electrodes may be adhered to thedilator segments 16 by a sticky probe or conductive epoxy ink.

Referring to FIGS. 1, 2A, and 2B, the actuating mechanism 14 is used tomove the dilator segments 16 from the collapsed state to the expandedstate. The actuating mechanism 14 may include an upper wedge 60 and alower wedge 62 axially moveable relative to one another. Generally, theupper wedge 60 is a conically shaped member with a tapered surface 63corresponding to the proximal tapered surface 34 of the dilator segments16 such that the tapered surface 63 of the upper wedge 60 is slidablealong the proximal tapered surface 34 of the dilator segments 16.Similarly, the lower wedge 62 is a conically shaped member with atapered surface 65 corresponding to the distal tapered surface 36 of thedilator segments 16 such that the tapered surface 65 of the lower wedge62 is slidable along the distal tapered surface 36 of the dilatorsegments 16. Relative axial movement of the upper wedge 60 and the lowerwedge 62 toward one another in turn causes the dilator segments 16 tomove from the collapsed state (FIG. 2A) to the expanded state (FIG. 2B).

The actuating mechanism 14 further includes an elongated rod 64extending from the lower wedge 62. The elongated rod 64 extends from thelower wedge 62, through the bore 20 of the dilator assembly 12, andthrough and beyond the upper wedge 60. In some embodiments, the lowerwedge 62 may be integral to the elongated rod 64. In some embodiments,the lower wedge 62 may be connected to the elongated rod 64.

Referring to FIGS. 3A and 3B, in some embodiments, the elongated rod 64may include a bore 70 extending the length of the elongated rod 64. Insome embodiments, the bore 70 may be sized to receive a probe 72(FIG. 1) or a K-wire (not shown). The axis of the probe 72 may becoaxial with the axis of the bore 70, and the probe 72 may be slidablyreceived within the bore 70. In some embodiments, the probe 72 may beintegrally formed as a part of the elongated rod 64.

The upper wedge 60 has an axial bore 94 for receiving the elongated rod64. The bore 94 is dimensioned to slidably receive the elongated rod 64such that the upper wedge 60 is slidable along and about the elongatedrod 64. To that end, the upper wedge 60 is provided with a rotationmember 96 to affect rotation of the upper wedge 60 in a way tofacilitate neural monitoring. Generally, a user may be capable ofrotating the rotation member 96 which in turn rotates the upper wedge60. The upper wedge 60 frictionally contacts the dilator segments 16such that rotation of the upper wedge 60 may rotate the dilator segments16 about the elongated rod 64 (e.g., 90°).

The rotation member 96 may include an outer surface 98 and an innersurface 100. In some embodiments, the outer surface 98 may be knurled orotherwise textured to facilitate gripping of the rotation member 96. Atleast a portion of the inner surface 100 of the rotation member 96 maybe threaded and mate with a threaded surface 104 of the upper wedge 60.

The rotation member 96 and the upper wedge 60 may form a groove 106wherein a ring member 108 may be positioned therein. Generally, the ringmember 108 remains stationary during rotation of the rotation member 96and the upper wedge 60. For example, the ring member 108 may remainstationary when the rotation member 96, the upper wedge 60, and thedilator segments 16 rotate about the longitudinal axis of the dilatorassembly 12.

As the ring member 108 may remain stationary during rotation of therotation member 96 and the upper wedge 60, in some embodiments, the ringmember 108 may further include a bearing. For example, the ring member108 may include a bearing 110, as illustrated in FIGS. 2A and 2B. Thebearing 110 may be any bearing capable of reducing friction between thering member 108 and the upper wedge 60. For example, the bearing 110 maybe a rolling element bearing, such as a ball bearing or low-frictionalwashers.

The actuating mechanism 14 may include an actuating handle 120. Theactuating handle 120 may be detachably connected to the elongated rod 64and the ring member 108 in suitable fashion, such as with pins 121. Insome embodiments, the actuating handle 120 may be permanently attachedto the elongated rod 64 and the ring member 108. Generally, theactuating handle 120 may include a first handle 122 and a second handle124 pivotally attached to one another at a pivot point 126.Additionally, the actuating handle 120 may include a spring 128.

The handles 122 and 124 affect translation of the upper wedge 60 withrespect to the lower wedge 62. In particular, the pivot point 126provides for the second handle 124 to translate downward movement of thering member 108. The ring member 108 in turn may displace the upperwedge 60 in a direction towards the lower wedge 62. As the distancebetween the upper wedge 60 and the lower wedge 62 decreases, the dilatorsegments 16 may be urged outwardly as the tapered surfaces 34 and 36 ofthe dilator segments 16 slide along the tapered surface 65 of the lowerwedge 62 and the tapered surface 63 of the upper wedge 60.

Referring again to FIGS. 2A and 2B, the actuating handle 120 may includean incremental indicator 143. The incremental indicator 143 may aid inidentifying expansion of the dilator assembly 12 and additionally aid inlocking expansion of the dilator assembly 12 at a desired expansion. Insome embodiments, the incremental indicator may be a ratchet 144 and afinger 152 capable of engaging the ratchet 144. The finger 152 may bespring-loaded and capable of incremental engagement with the ratchet144. With the finger 152 engaged with the ratchet 144, the dilatorassembly 12 is locked in a particular state (i.e., expanded state). Bydisengaging the finger 152 from the ratchet 144, the spring 128 mayreturn the actuating handle 120 to a neutral position so as to returnthe dilator assembly 12 to the collapsed state.

In some embodiments, the ratchet 144 may include associated labels. Inone example, the labels may identify the diameter of the dilatorassembly 12 (e.g., 6 mm). In some embodiments, the labels may correspondto a pre-determined level of movement. For example, the labels mayinclude a number a user will associate with a type of movement. In thisexample, the label “Level I” may correspond to a first expandedconfiguration of the dilator assembly 12, and the label “Level II” maycorrespond to an a second expanded configuration of the dilator assembly12.

FIG. 7 illustrates another exemplary actuating handle 160 for use withinthe dilator system 10 of FIG. 1. The actuating handle 160 may include afirst handle 162 and a second handle 164 with an axis or pivot point166. Additionally, the actuating handle 160 may include a threaded rod168 for varying the distance between handles 162 and 164 about the pivotpoint 166.

The threaded rod 168 may be connected to the first handle 162 and thesecond handle 164 with brackets 170 a and 170 b, respectively. Eachbracket 170 a and 170 b may include a hole for threading the threadedrod 168 therein. For example, a proximal end of the threaded rod 168 maybe threaded through the hole of the bracket 170 a, and a distal end ofthe threaded rod 168 may be threaded through the hole of the bracket 170b.

A knob 178 may be included on the threaded rod 168 between the brackets170 a and 170 b. The knob 178 may be formed with small ridges orundulations aiding in gripping of the knob 178. Rotation of the knob 178may increase or decrease the distance between the handles 162 and 164about the pivot point 166.

An incremental indicator 180 may aid in identifying expansion of thedilator assembly 12 when used in the dilation system of FIG. 1. Forexample, two or more labels may be provided on the incremental indicator180 to illustrate distances of expansion of the dilator assembly 12during use as described herein.

Referring to FIGS. 2A and 2B, in use, the actuating handle 120 may beattached to the elongated rod 64 and the ring member 108, and may aid indilating dilator segments 16 as the dilator assembly 12 is progressed upto surgical site, such as a disc annulus. The dilator segments 16 maymove from the collapsed state (FIG. 2A) to the expanded state (FIG. 2B).In particular, during expansion, the actuating handle 120 may hold theelongated rod 64 substantially stationary while applying a translationalforce upon the ring member 108 and upper wedge 60 such that the taperedsurface 34 of the inner side 32 of the dilator segments 16 slide alongthe tapered surface 63 of the upper wedge 60. To that end, the taperedsurface 36 of the inner side 32 of the dilator segments 16 may alsoslide along the tapered surface 65 of the lower wedge 62 decreasing thedistance between the upper wedge 60 and the lower wedge 62 and forcingthe dilator segments 16 outwardly from the longitudinal axis.

In some embodiments, a K-wire (not shown) may be inserted through thebore 20 of the dilator assembly 12 to guide the dilator assembly 12 tothe surgical site. In some embodiments, the K-wire may be insertedthrough the elongated rod 64.

FIG. 8 illustrates a flow chart 200 of an exemplary method for formingan access opening through a muscle in a patient's spine. In a step 202,the probe 72 or a K-wire may be inserted into the muscle. In a step 204,an electrical pulse via an electromyograph (EMG) may be transmitted intothe probe 72 in order to locate a safe zone in the muscle. In a step206, the actuating handle 120 may be connected to the dilator assembly12 via the elongated rod 64 and the ring member 108. In a step 208, thedilator assembly 12 may be inserted through the muscle toward thepatient's spine guide by the sliding engagement of the probe 72. Duringinsertion through the muscle, the dilator assembly 12 may also use theelectrode assembly 40 of the dilator assembly 12 for nerve surveillance.In some embodiments, the rotation member 96 may also provide rotation bya user such that dilator segments 16 having electrode assemblies 40included therein may rotate about the elongated rod 64 and monitornerves exterior to the dilator assembly 12. It should be noted thatrotation of the dilator assembly 12 via the rotation member 96 isindependent of the actuating handle 120.

In a step 210, the dilator assembly 12 may be incrementally expandedfrom the collapsed state to a desired expanded state. In particular, thedistance between the upper wedge 60 and the lower wedge 62 may bedecreased forcing the dilator segments 16 outwardly. In someembodiments, a user may compress the first handle 122 and the secondhandle 124 of the actuating handle 120. Compression of the first handle122 and the second handle 124 may provide translational movement of theupper wedge 60 relative to the lower wedge 62 in that the proximalsurface 34 of the inner side 32 of each dilator segment 16 may slidablymove along the tapered surface 63 of the upper wedge 60. Additionally,the distal tapered surface 36 of the inner side 32 of each dilatorsegment 16 may slidably move along the tapered surface 65 of the lowerwedge 62. The sliding movement of the dilator segments 16 along thetapered surfaces 65 and 63 of the lower wedge 62 and the upper wedge 60,respectively, may force the dilator segments 16 outwardly.

In a step 212, the dilator assembly 12 may be rotated via the rotationmember 96 in a way to verify the dilator assembly 12 is in a safe zone.By way of example, the dilator assembly 12 may rotated through an angleof approximately 90 after each incremental increase until the dilatorassembly 12 has been expanded to the desired expanded state.

To return the dilator segments 16 to a neutral position, compression ofthe actuating handle 120 may be reduced such that the spring 128 of theactuating handle 120 returns the upper wedge 60 to its starting positionvia translational movement of the ring member 108.

From the above description, it is clear that the inventive conceptsdisclosed and claimed herein are well adapted to carry out the objectsand to attain the advantages mentioned herein, as well as those inherentin the invention. While exemplary embodiments of the inventive conceptshave been described for purposes of this disclosure, it will beunderstood that numerous changes may be made which will readily suggestthemselves to those skilled in the art and which are accomplished withinthe spirit of the inventive concepts disclosed and claimed herein.

What is claimed is:
 1. A dilation system, comprising: a dilator assemblycomprising a plurality of dilator segments, each dilator segment havinga proximal end, a distal end, an inner side, and an outer side, theinner side of each of the dilator segments having a proximal taperedsurface extending from the proximal end toward the distal end and adistal tapered surface extending from the distal end toward the proximalend; and an actuating mechanism having an upper wedge and a lower wedgeaxially moveable relative to one another, the upper wedge having atapered surface corresponding to the proximal tapered surface of thedilator segments such that the tapered surface of the upper wedge isslidable along the proximal tapered surface of the dilator segments andthe lower wedge having a tapered surface corresponding to the distaltapered surface of the dilator segments such that the tapered surface ofthe lower wedge is slidable along the distal tapered surface of thedilator segments, the upper wedge and the lower wedge being axiallymoveable relative to one another in a way to cause the dilator segmentsto move between a collapsed state and an expanded state.
 2. The dilationsystem of claim 1, wherein the actuating mechanism further includes anactuating handle comprising: a first handle; and a second handlepivotally connected to the first handle and configured in such a waythat movement of the first handle and the second handle relative to oneanother causes translational movement of the upper wedge relative to thelower wedge.
 3. The dilation system of claim 2, wherein the actuatingmechanism further comprises a rod extending from the lower wedge andbeing pivotally connected to the first handle.
 4. The dilation system ofclaim 3, the upper wedge is slidably received over the rod.
 5. Thedilation system of claim 2, wherein the actuating handle includes anincremental indicator for identifying the diameter of the dilatorassembly.
 6. The dilation system of claim 2, wherein the actuatinghandle includes a ratchet having at least two teeth forming a groove,and a finger capable of being slidably received within the groove. 7.The dilation system of claim 1, wherein the dilator segments are biasedin the collapsed state.
 8. The dilation system of claim 1, wherein atleast one of the dilator segments has a slot formed in the outer surfacethereof for receiving a probe.
 9. The dilation system of claim 1,wherein at least one of the dilator segments includes an electrodeassembly.
 10. The dilation system of claim 1, wherein the upper wedge isrotatably connected to the second handle of the actuating mechanism in away that rotation of the upper wedge rotates the dilator assembly. 11.The dilation system of claim 4, wherein the upper wedge is rotatablyconnected to the second handle of the actuating mechanism in a way thatrotation of the upper wedge rotates the dilator assembly.
 12. A methodof forming an access opening through a psoas muscle to a patient'sspine, comprising the steps of: inserting a guide into the psoas muscleto locate a safe zone in the psoas muscle; laterally inserting a guidethrough the psoas muscle such that a guide tip is proximate thepatient's spine; inserting a dilator assembly through the psoas muscleand toward the patient's spine guided by sliding engagement of theprobe, the dilator assembly comprising a plurality of dilator segments;and expanding the dilator segments radially from a collapsed state to anexpanded state.
 13. The method of claim 12, wherein the step ofexpanding the dilator segments comprises applying an axial compressiveforce to the dilator segments.
 14. The method of claim 13, wherein thestep of applying an axial compressive force further comprises: moving anupper wedge and a lower wedge relative to one another to cause a taperedsurface of the upper wedge to slidably move along a correspondingtapered surface at the proximal end of the dilator segments and atapered surface of the lower wedge to slidably move along acorresponding surface at the distal end of the dilator segments.
 15. Themethod of claim 12, wherein the guide is a stimulating probe, andwherein the method further comprises inserting the stimulating probeinto the psoas muscle to locate a safe zone in the psoas muscle prior toinserting the dilator assembly through the psoas muscle.
 16. The methodof claim 12, wherein at least one of the dilator segments includes anelectrode assembly, and wherein the method further comprises the stepsof: incrementally expanding the dilator assembly; and rotating thedilator assembly to verify the safe zone in the psoas muscle prior toeach incremental expansion.